Oxygen is critical to human life. Each cell, tissue, and function of the human body requires oxygen. Without oxygen, cells cannot function, repair, and restore. A shortage of oxygen, or hypoxia, can thus cause several problems, some of which carry immediately noticeable effects. Examples of symptoms of hypoxia may include, but are not limited to, nausea, headache, fatigue, and shortness of breath. In severe cases, hypoxia may result in loss of consciousness, seizures, coma, and even death.
High altitudes reduce the partial pressure of oxygen in the lungs. Exposure to a reduced oxygen partial pressure environment, such as in a pressurized aircraft, can thus result in hypoxia. The pressure in an aircraft cabin at altitude is typically maintained at the pressure one would experience at about 7,000 feet (approximately 11 psi). A similar effect is observed in geographic locations at high altitudes. For example, the partial pressure of oxygen is reduced for a high altitude city, such as Denver, Colo., when compared to the partial pressure of oxygen of a city at sea level, such as New Orleans, La. The “station pressure” in Denver is typically about 23-24 inches/hg (about 12 psi) versus the “station pressure” at sea level, which is typically around 30 inches/hg (about 15 psi).
Oxygen accounts for approximately 21% of dry air and the partial pressure of oxygen will decrease in proportion to the decrease in ambient pressure. Accordingly, and by way of example, the partial pressure of oxygen in ambient pressure at sea level is approximately 3.1 psi and will thus proportionally decrease to approximately 2.3 psi in the pressurized aircraft cabin.
A person's sensitivity to reduced oxygen partial pressure environments and/or high altitudes can generally be classified into one of two categories—normal healthy persons and persons having special sensitivities. A normal healthy person will typically not experience side effects from exposure to reduced oxygen partial pressure, such as that observed during air transport on an aircraft at altitude or at a geographic location having a high altitude. A small subset of healthy persons, however, will experience some side effects from exposure to reduced oxygen partial pressure environment, such as that observed during air transport on an aircraft at altitude. This may typically be described as “feeling lousy” after a flight. The other category of individuals includes those with special sensitivities. These persons are individuals who more often than not have pre-existing neurological conditions, such as epilepsy. These persons may or may not experience immediate episodes or symptoms from being at a high altitude, but may instead be susceptible to delayed effects that present following a period of exposure to a reduced oxygen partial pressure environment. One example is that persons with certain forms of epilepsy may not experience symptoms or episodes while exposed to a reduced oxygen partial pressure environment, but instead may have an increased risk of experiencing seizures in a relatively short period of time, up to a few days, following the exposure.
Presently, there are a number of techniques to treat the contemporaneous effects of oxygen deprivation observed from exposure to a reduced oxygen partial pressure environment. One such well-known technique is the administration of supplemental oxygen. When an individual becomes hypoxic after suffering some degree of oxygen deprivation, supplemental oxygen is then supplied to compensate for the observed oxygen deprivation. However, this technique is only applied to address the contemporaneous or immediate effects resulting from the oxygen deprivation. It is not used preventatively to minimize or eliminate the delayed effects of exposure to reduced oxygen partial pressure.
Another similar, well-known technique is administering supplemental oxygen to relieve acute symptoms from exposure to a reduced oxygen partial pressure environment to facilitate/maintain pilot concentration at altitude. In this regard, it is known to provide aircraft pilots with supplemental oxygen to deter the occurrence of a loss of consciousness and/or concentration at high altitudes upon exposure to reduced oxygen partial pressure. Much like the above-mentioned methods for treating hypoxia, supplemental oxygen is provided to abate the immediate effects of oxygen deprivation.
Supplemental oxygen administration also has known applications in treating persons having pre-existing pulmonary conditions. Similar to the treatment of hypoxia, the use of supplemental oxygen for persons having pre-existing pulmonary conditions is therapeutic in nature and contemporaneous to the known condition.
Known oxygen delivery devices are operable to supply oxygen to a person according to one of two ways—at a fixed flow rate or on demand. When oxygen is supplied at a fixed flow rate, the oxygen is typically delivered at a set volume and a set flow rate, regardless of the individual's need for oxygen. This is true when the individual's demand for oxygen is either higher or lower than the amount of oxygen delivered by the set flow rate. In an on demand delivery device, oxygen is supplied to the individual during an inhalation cycle. On demand delivery devices tend to conserve more oxygen than the constant flow rate devices since oxygen is only supplied when the individual inhales rather than continuously free flowing throughout the individual's respiration cycle.
Supplying oxygen also requires controlling the flow rate to meet an individual's demand. This can be effectuated according to any of the several techniques for estimating demand known to those of skill in the art. In some techniques, one or more pressure sensors are placed in relative proximity to an individual's breathing location (e.g., nose or mouth) to measure the ambient pressure and the individual's breathing pressure. The breathing pressure represents the air inhaled and/or exhaled by the individual during a respiration cycle. The measured pressure values are then used to regulate the flow rate. It is common practice for the flow rate to be adjusted such that the pressure differential between the ambient pressure and the breathing pressure is zero. Other exemplary methods for estimating the demand for oxygen involve measuring the amount of carbon dioxide exhausted by the person, measuring the rate of breathing, measuring the flow rate, and measuring the level of activity of a person.
It is also known to control the demand for oxygen by varying the concentration of the oxygen being administered. This is typically effectuated by providing a supply of ambient air mixed with pure oxygen. Since the concentration of oxygen decreases as altitude increases, compensation for this differential can be achieved by increasing the proportion of pure oxygen administered to an individual for a higher altitude.
As indicated above, there are several known techniques for treating the immediate effects of oxygen deprivation. But, these techniques do not consider the negative effects that may occur subsequent to exposure to a reduced oxygen partial pressure environment. Accordingly, there exists a need to develop a preventative measure or technique to compensate for an exposure to a reduced oxygen partial pressure environment in order to minimize or eliminate the occurrence of delayed effects from the exposure, specifically in persons having special sensitivities.